Atapa vs CircadianShield: Mac and Windows at $47, or Mac only at $12?
Choose CircadianShield if you want one licence for Mac and Windows and a dashboard that reports melanopic light. Choose Atapa if you are on an M5 Pro or M5 Max, or want readable deep red at 500K for $12 once. CircadianShield's own site said on 28 October 2026 that M5 has not been tested yet; its warmest setting is 1800K.
Kevin Hofmann, maker of Atapa. Updated . We make Atapa. Corrections welcome at hello@atapa.app.
CircadianShield is a paid-once warmth app for Mac and Windows that leads with melanopic light, which is the right thing to lead with. This page is about where the two apps differ, with the date each fact was read.
Side by side
| Criterion | CircadianShield | Atapa |
|---|---|---|
| Price | $47 once, up to 2 computers; no free trial; 30-day refund (2026-10-28) | $12 once, all of your own Macs; 14-day trial without a card; 14-day refund |
| Platforms | macOS 14 and 15 on M1 through M4 Max, and Windows 10 or later (2026-10-28) | macOS 14 or later, Apple silicon; Intel not supported in 1.0 |
| M5 Pro | “M5 has not been tested yet”, its own site (2026-10-28) | Works, 6500K to 500K on our M5 Pro (2026-10-29, macOS 27.2) |
| Warmest | 1800K (2026-10-28) | 500K |
| Readable red | Not described (2026-10-28) | Yes, below 1500K |
| Dims below the lowest brightness step | Not described (2026-10-28) | Yes, 5% floor by default |
| Melanopic figure | Dashboard | One evening ring, an estimate |
| Automation | Not listed (2026-10-28) | Shortcuts, Focus filter, URL scheme, CLI |
| Network use | Anonymous usage statistics, off by default (2026-10-28) | No network code |
Where CircadianShield leads
One licence covers a Mac and a Windows PC, up to 2 computers. Its melanopic dashboard is more detailed than Atapa’s single ring. Its refund window is 30 days against Atapa’s 14. If you split your evenings between a MacBook and a Windows desktop, it is the only app on our comparison besides f.lux that covers both, and f.lux is free but does nothing on an M5 Pro.
Where it stops
Its warmest setting is 1800K, which is amber. Atapa’s Gentle intensity ends the night at 1900K, so CircadianShield’s maximum is roughly Atapa’s mildest evening. Atapa’s Warm and Deep red intensities go to 1200K and 500K, and from 1500K down Readable red keeps links and icons visible.
On the M5 Pro and M5 Max, CircadianShield’s own site says M5 has not been tested yet (read 2026-10-28). We have not installed it on our M5 Pro, so we do not say whether it works there. Atapa does: tested on a 14-inch M5 Pro, macOS 27.2, on 2026-10-29, down to 500K. The one-minute check for the M5 gamma bug is on the M5 page.
Melanopic numbers, both estimates
CircadianShield reports melanopic light in a dashboard. Atapa reports one ring, “about x% less alerting light”, estimated from CIE S 026 weights on a P3 panel model: blue carries about 72% of a white screen’s melanopic signal, green about 28%, red almost none. At 2700K and 90% brightness the ring says about 82% less than an untouched screen. Both are estimates from the display’s output, not measurements of your eyes or your sleep. Atapa does not claim a sleep outcome, and the science page explains why.
Privacy
CircadianShield sends anonymous usage statistics, off by default. Atapa has no network code: no account, no update check, no analytics, and the licence key is an offline signed string. Both are paid once.
Price
CircadianShield is $47 once for up to 2 computers, with no free trial and a 30-day refund. Atapa is $12 once for all of your own Macs, with a 14-day trial that asks for no card and a 14-day refund. After the trial Atapa keeps working; from day 29 without a key, warmth stops at 2700K and everything else continues.
Choose CircadianShield if
You need Mac and Windows on one licence, you want a detailed melanopic dashboard, and 1800K is warm enough. If you are on an M1 through M4 Mac, its own site lists your chip as supported.
Choose Atapa if
You are on an M5 Pro or M5 Max, you want deep red at 500K that stays readable, or you want the lower price and no network code. Intel Macs are not supported in 1.0, and there is no Windows build.
Questions
Does CircadianShield work on M5 Pro and M5 Max?
Its own site lists Apple silicon M1 through M4 Max and says M5 has not been tested yet, read on 2026-10-28. We have not installed it on our M5 Pro, so this page does not say either way. Atapa was tested on a 14-inch M5 Pro with macOS 27.2 on 2026-10-29 and changed the screen down to 500K. If CircadianShield publishes an M5 result, we will add the date here.
What does each one cost?
CircadianShield is $47 once for up to 2 computers, Mac and Windows, with a 30-day refund and no free trial, read 2026-10-28. Atapa is $12 once for all of your own Macs, with a 14-day trial that asks for no card and a 14-day refund. If you need Windows, only CircadianShield covers it.
How warm does each one go?
CircadianShield's warmest published setting is 1800K, read 2026-10-28. Atapa goes to 500K, and below 1500K it folds blue and green into red so links and icons stay visible. Atapa's three evening intensities end the night at 1900K, 1200K and 500K; the Gentle stop is close to CircadianShield's warmest.
Which one is more private?
CircadianShield sends anonymous usage statistics, off by default, per its site on 2026-10-28. Atapa has no network code at all: no account, no update check, no analytics, and the licence key is checked on the Mac with an offline signature. Both are paid once rather than by subscription.
Does either one measure melanopic light?
CircadianShield has a melanopic dashboard and builds its marketing around that figure. Atapa shows one evening ring: an estimate of melanopic light compared with an untouched screen, using CIE S 026 weights on a P3 panel model (blue about 72%, green about 28%, red almost none). Neither number is a sleep measurement, and Atapa does not claim one.